The long-range goal of this proposal is to understand the role cholecystokinin (CCK) plays in health and disease. This specific proposal concentrates on the levels of the CCK peptides, their receptors in various tissues, and peptide-receptor interactions. There are two specific and inter-related aims: 1) development of methodology to quantify CCK and its molecular species, and 2) development of methodology to characterize CCK receptors in various tissues both functionally and biochemically. Quantification of CCK will be attempted using a) radioimmunoassay with conventional polyclonal antisera, b) radioimmunoassay with monoclonal antisera, and c) radioreceptor assay. Molecular species of CCK will be separated by high performance liquid chromatography. CCK receptors will be characterized functionally using ligand binding techniques, and biochemically using affinity labeling and chemical crosslinking. These approaches will add basic information about this physiologically important gastrointestinal hormone, and provide means to directly evaluate the role this hormone plays in health and disease. Screening of CCK and its receptor function may permit identification of abnormalities which mediate pathologic processes in man.